In all honesty I think your over thinking it the loop at the bottom is kind of useless. Just have the intake for the s1 lower then the lowest point of where the water till sit when draining the tank. Then make sure to put a screen cover on the inlet of vectra
-Also i highly suggest if you really want to do a close type wave setup then drill the back wall of the tank and do the closeloop properly.
-Also I don’t know of any solenoids that are 1/2”min can be under water.
I’m running a closeloop on my 150. I use a vectra m1 as the pump and love it. The back wall of my tank is drilled for a 1.5” bulkhead. Then 1.5” bulkhead is the inlet for the vectra
The water is drawled in through the bulkhead then through the vectra and T’ed off to feed 2 seaswirls in each corner
And as you can see in this pic I added a second T so if I wanted to add a 3rd seaswirl.
But if I added a few ball valves and another T I could possibly do what your trying to do with your diagram.
But personally I like to know how much water I’m taking out of my tank when doing a water change.
So when I do water changes I make 30g of SW a few days before in a food grade water barrel. Then I have a second 35g trash can that has wheels on the bottom. I’ve marked 30g off inside the trash can and I drain the tank till I’ve hit 30g in the trash can. I then dump that old SW in the gutter after filling the tank with the fresh SW.
Here’s one flaw I see with how your planning. What if you walk away for a second and drain more water from the tank then what you have to fill. At least if you fill a bucket or trash can you still have old SW you can use to fill if you didn’t make enough new SW